These
lines indicate the shape of the surface upon which osteoblasts began
laying down fresh lamellae after osteoclasts had excavated a
channel throught the bone.

The patterns of lamellae reflect the history of bone remodelling. Osteons
with complete concentric lamellae are the most recently formed. Other
lamellae, which terminate abruptly against a cement line, are the fragmentary
remains of former osteons that have been partially removed and replaced during
remodelling.

Number 1
indicates a recently formed osteon.

Number 2
indicates a somewhat older osteon, as demonstrated by the encroachment of
osteon 1.

Number 3
indicates interstitial lamellae, representing the remnants of still older
osteons.